Successively joinable carbon electrode for gouging metallic articles

ABSTRACT

A joinable slender carbon electrode having its surface coated with copper, one end of which is formed into a substantially coaxial projecting portion and the other end into a substantially coaxial socket portion, whereby said electrode is improved in the following respects: I. A projection consisting of a cylindrical base part coated with a slightly tapered formation of a thin copper layer which is applied in continuation of the copper layer plated on the carbon electrode body, and a noncoated frustoconical top part integrally formed with said base part. II. A socket shaped like said projection wherein there is a slotted cut throughout its open cylindrical part, and the inner wall of said cylindrical part is uniformly coated with a thin copper layer which is applied in continuation of the copper layer plated on the carbon electrode body.

United States Patent [7 21 Inventor Masao Ando Ogaki-shi, Japan [21] Appl. No. 3,007

[22] Filed Jan. 15, 1970 [45] Patented Jan. 4, 1972 [73] Assignee Ibigawa Electric Industry Co., Ltd.

Ogaki-shi, Japan [32] Priority Feb. 8, 1967 Jap Continuation-impart of application Ser. No. 657,195, July 31, 1967, now abandoned. This application Jan. 15, 1970, Ser. No. 3,007

[54] SUCCESSIVELY JOINABLE CARBON ELECTRODE FOR GOUGING METALLIC ARTICLES 6 Claims, 3 Drawing Figs.

[52] U.S.(l 313/357, 219/145,?913/355 [51] Int. Cl ..B23k35/04, B23k35/22 [50] FieldoiSearch 313/354, 355,357;2l9/145 Primary ExaminerDavid Schonberg Assistant ExaminerPaul A. Sacher AttorneyFlynn & Frishauf ABSTRACT: A joinable slender carbon electrode having its surface coated with copper, one end of which is formed into a substantially coaxial projecting portion and the other end into a substantially coaxial socket portion, whereby said electrode is improved in the following respects:

1. A projection consisting of a cylindrical base part coated with a slightly tapered formation of a thin copper layer which is applied in continuation of the copper layer plated on the carbon electrode body, and a non-coated frusto-conical top part integrally formed with said base part.

11. A socket shaped like said projection wherein there is a slotted out throughout its open cylindrical part. and the inner wall of said cylindrical part is uniformly coated with a thin copper layer which is applied in continuation of the copper layer plated on the carbon electrode body.

alsaaloss PATENTED MI 4 BR FIG. 2

SUCCESSIVELY JOINABLE CARBON ELECTRODE FOR GOUGING METALLIC ARTICLES CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of my copending U.S. Pat. application Ser. No. 657,195 filed July 31, 1967, now abandoned, and assigned to the same assignee as the present invention.

BACKGROUND OF THE INVENTION This invention relates to a slender carbon electrode, and especially to a successively joinable carbon electrode which is useful for gouging or blasting steel or other metallic articles.

The carbon electrode which has been widely used for such purpose comprises a copper-coated carbon electrode having a diameter of from one-fourth to 1 inch and a length of approximately 1 foot. As is well recognized in the art, when a strong electric current such as the one of from 500 to 1,500 amperes is passed through such carbon electrode, it has a tendency to flow essentially through the surface layer of the electrode. The copper coating is provided for the purpose of reducing the electric resistance of the surface layer, thereby to improve its current carrying capacity and prevent the electrode from being overheated.

When used in gouging the surface of any steel or other metallic articles, said rod of carbon electrode is gripped by a suitable holder, through which electric current is supplied to the electrode to spark an electric are between the tip of the electrode and the surface of said article. The surface metal is melted by the arc fire to be blown off by a high pressure air supplied from the holder. The successive shifting of the electrode tip along the surface of the metallic article at a fixed interval of time enables the surface to be cut away to a definite depth. This technique is also adaptable to blast OK the undesired burrs of any metallic casting.

While the electrode is operated, it is necessary to keep the holder at least more than 2 inches apart from the arc fire in order to prevent it from being seriously damaged by high temperature flames. Therefore, as the electrode is gradually consumed, the holder must be moved toward the upper end of the electrode. The electrode must be finally discarded when it becomes too short, and this normally results in a loss of at least 20 percent of the electrode material.

If the electrode could be connected to the next one directly and coaxially while being used, the above-mentioned loss would be eliminated. Large sized carbon electrodes used in electric metal refining are provided with female and male screw threads at their opposite ends so that they may be coupled together by meshing said screw threads. However, electrodes of small diameter, such as those used for gouging, can not be practically coupled by means of screw threads in view of their small mechanical strength.

An example of successively joinable rod of carbon electrode for such purpose is disclosed in U.S. Pat. 3,030,544. One end of the electrode is coaxially fonned into a frustoconical projecting portion, and the other end into a socket portion shaped like said projection. The forcible insertion of the projection of one electrode into the socket of another causes these electrodes to be coupled together by the frictional force prevailing between their carbon surfaces. It is described in said patent that the preferable tapering degree of the conical shape has an included angle of from 2 to In this case, a copper-tocopper surface contact is not suitable because it gives a smaller frictional force than a carbon-to-carbon surface contact.

Carbon electrodes constructed as described above can indeed be coupled very easily. However, there is produced an unstable are because of great and unsettled electrical resistance between the carbon-to-carbon contact surfaces. Furthermore, temperature at the connected part of the electrode assembly is liable to rise very high due to said electrical resistance, thereby resulting in the melting off of the coated copper on that part of the electrode body which is disposed close to said connection, and in consequence the increased oxidation loss of carbon material. When the connected part comes near the arc during operation, the force with which the projection and socket are joined is likely to be considerably reduced because the arc causes the socket to be more heated and expanded than the projection, thereby resulting in the falling off of the tip part from the electrode assembly by the compressed air blown from the holder.

Another form of a successively joinable carbon electrode of this kind is described in U.S. Pat. No. 3,399,322, filed Oct. 2 l 1965 and assigned to the assignee of the instant application. In scarcely case, the coaxial cylindrical projection of the electrode is coated with a copper layer which is applied in continuation of that coated on the electrode body, and the coaxial cylindrical socket is also coated with a similar copper layer. The diameter of the projection is slightly larger than the inner diameter of the socket, and said cylindrical projection has an axial slot to give resilience thereto. The forcible inserting of the projection of one electrode into the socket of another allows these electrodes to be coupled together firmly by the resilient force of the cylindrical projection.

Carbon electrodes joined as described above indeed enable a very stable arc to be produced because the copper-to-copper contact leads to good condition of electric current, and temperature at the connected part of the electrode assembly scarcely rises. Moreover, even when the connected part is brought near the arc during operation, the falling off of the tip part from the electrode assembly does not occur because the resilient force of the cylindrical projection always acts effectively.

However, it is not easy in the case of said US. Pat. No. 3,399,322 to connect two electrodes securely because of the insufficient resilience offered by said slot formed throughout the cylindrical projection. Even though the slot is cut through the projection, the resilient force and mechanical strength of the carbon electrode are not appreciably great, thus often resulting in its breakage when it is inserted forcibly. On the contrary, if the diameter of the projection is the same as, or smaller than that of the socket, the resilient force will not act at all, and the firm coupling of two electrodes can not be achieved. Therefore, the precise working of said suitable diameters is required for good coupling, but such machining is troublesome and uneconomical.

SUMMARY OF THE INVENTION An object of the present invention is to provide a novel electrode assembly which is free from the aforementioned shortcomings encountered with U.S. Pat. No. 3,030,544 and U.S.

Pat. No. 3,399,322, and has a good nature of being easily and firmly joined and allowing electric current to be smoothly conducted.

Another object of the present invention is to produce such good quality electrode at low cost.

These objects may be attained by partially utilizing the above-mentioned two U.S. patents, but adding a new device for the finn joining and smooth conduction of electric current.

According to the present invention, one end of the carbon electrode is coaxially formed into a projection having a cylindrical base part and a frustoconical top part. Said base part of the projection is coated with metallic copper, which is joined to the copper coating on the outer surface of electrode body, and the copper coating layer on said cylindrical base part has a slightly tapered figure. Said frustoconical top part of the projection is not provided with any slotted cut. The cylindrical open part of said socket is provided with a slotted cut which serves to afford good resilience to it. The inner wall of the cylindrical open part of the socket is coated uniformly with metallic copper, which is joined to the copper coating on the outer surface of electrode body, and inner surfaces of the frustoconical part of the socket is not coated with copper. The top diameter of said cylindrical base part of the projection is slightly larger than the inner diameter of said cylindrical open part of the socket.

The feature of the invention which are believed to be novel are set forth with particularity in the appended claims. The invention itself, however, as to its organization together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an elevational view of a carbon electrode assembly clamped by a holder for gouging the surface of a steel work;

FIG. 2 is an elevational view, partly in section, of a carbon electrode assembly embodying this invention; and

FIG. 3 is a schematic and sectional elevation of an electrolytic cell showing the manner in which a copper layer is electrolytically coated on the surface of the carbon electrode of the present invention.

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 of the accompanying drawing presents a carbon electrode assembly for gouging the surface of steel work comprising a partially consumed stubb l 1 of carbon electrode and a new carbon electrode 21 which are suitably jointed at the connecting part 10. The carbon electrode assembly is gripped by a holder 1 to which there is supplied an electric current of large amperes through a conducting line 2. The holder 1 can be loosened and moved to any new gripping position as the electrode is consumed or burnt up by an electric arc 4 generated between the lower end of the electrode assembly and the surface of the steel work 5. The steel work 5 is connected to the other terminal of an electric source by another conducting line 6. The metal melted by the heat of electric are 4 is blown off by the compressed air spurting out of the outlet port 3 of the holder 1. If, therefore, there is applied an arc successively over the surface of the steel work, its surface layer can be removed to a predetermined depth. This is the socalled gouging process.

FIG. 2 shows the construction of a carbon electrode of the present invention. Carbon electrodes to be connected together are of the same shape and size. One end of the electrode 11 or. 21 is formed into a substantially coaxial socket portion 12 comprising a cylindrical opening part 13 and a frustoconical bottom part 14. The inner wall and the annual end side of the cylindrical opening part 13 are coated with a thin and uniform copper layer which is applied in continuation of a copper layer 15 or 25 plated on the carbon electrode body 11 or 21. The cylindrical opening part 13 had a slot 16 or 26 cut throughout its sidewall. Although the thickness of the copper coating is shown exaggerated in the figures, actually it may be approximately 0.004 inch. There is no copper coating on the inside of the frustoconical bottom part 14.

The opposite end of the electrode 11 or 21 is fonned into a substantially coaxial projection 22 which corresponds to said socket l2, and comprises a cylindrical base part 23 and a frustoconical top part 24 integrally formed with said base part 23. The outer surface of the base part 23 and the carbon body 21 are coated continuously with a thin copper layer. There is no copper coating on the surface of the frustoconical top part The most important characteristic of the present invention is that there is coated a copper layer on the cylindrical part of the projection not in a uniform thickness but in a slightly tapered form as viewed from the end of the carbon electrode body, as shown in FIG. 2. The formation of such tapered copper layer may be easily effected by the process shown in FIG. 3 in principle. According to this process, an electrolytic cell 32 is filled with an electrolyte 31 of suitable composition. There is immersed in the electrolyte 31 a cylindrical copper metal 33, used as an anode, and an uncoated carbon electrode 34 of the present invention, as a cathode, in such a manner that the level 35 of the electrolyte 34 is positioned at the substantially middle part of the cylindrical base part 36 of the projection. When electrolysis is conducted by an ordinary method, there is electrolytically coated a copper layer 37 on said cylindrical base part 36 of the projection in a slightly tapered form as illustrated. The reason is assumed to be that the level 35 of the electrolytic bath is agitated in a slightly rippled state and cause to more occasionally a little upward along the surface of said base part 36. The surface tension between the electrolyte and the carbon may also participate in this elevation of the electrolyte.

The diameter of said cylindrical base part 23 is preferably from 60 to 70 percent of that of the electrode body 11 or 21, and the inner diameter of the cylindrical opening part 13 of the socket 12 is made slightly smaller than the terminal diameter of the frustoconical top part 24 of the projection 22. The total length of the projection 22 is preferably from to percent of the electrode diameter, while the total depth of the socket 12 is made a little longer than the total length of the projection 22, and the length of the cylindrical opening part 13 of the socket I2 is made a little smaller than that of the cylindrical base part 23 of the projection 22. Further it has been experimentally recognized that, for the purpose of the present invention, the preferable taper degree, which must be exactly the same for the frustoconical parts of both socket and projection, should have an inclined angle of from 12 to 18.

When two carbon electrodes of the present invention are to be joined, the frustoconical top part 24 of the projection 22 is inserted into the socket 12 first with no frictional force, and then the cylindrical base part 23 of the projection 22 is forcefully pushed into the cylindrical opening part 13 of the socket 12. The first insertion of the frustoconical top is very easily performed due to absence of any friction whereas the subsequent introduction of the base part is forcibly effected against a frictional force caused by the different diameters of the open part 13 of the socket and the base part 23 of the projection 22. However, thelatter introduction is smoothly carried out by the resilience of the cylindrical opening part 13 afforded by the slot 16 cut therethrough. In this case there is obtained a far greater resilience than is possible with the previous invention, US. Pat. No. 3,399,322, and the mechanical strength of the cylindrical opening part 13 is fully sufficient to withstand said second introduction, so that there is no possibility of said open part 13 of the socket being damaged.

With the previous invention, US. Pat. No. 3,399,322, the projection was liable to be broken at the slotted part during its forced insertion due to the small mechanical strength of said part. Even where there occurred no such breakage, it has been discovered that the copperto-copper contact was not so good as desired. This was supposed to result from the fact that the slotted part of the projection was slightly deflected inward by the forced insertion, causing the copper-to-copper contact between the projection and socket to be only realized linearly and not in the form of a surface contact.

The present invention, however, eliminates the possibility of either the projection or the slotted part of the socket being damaged or broken because of their cylindrical formation. Further, the aforementioned slightly tapered copper layer coated on the base part of the projection permits the coppercoated parts of both base part of the projection and cylindrical part of the socket to contact each other over the entire surface. Said slightly tapered formation of the copper layer is so designed as to allow for the deformation of cylindrical part of the socket which would be caused with the aid of slotted cut when the projection is forcibly pushed into said socket.

When further pushed, the tapered surface of the frustoconical top part 24 is aligned with that of the frustoconical bottom part 14, and the last strong insertion accompanied with some rotation of a new electrode enables two electrodes to be very firmly coupled by a frictional force caused by the carbon-tocarbon surface contact of both frustoconical parts, and the resilient force ofiered by the slotted cut which is slightly opened when the aforesaid forcible pushing is carried out.

The present invention assures a full copper-to-copper contact, allowing electric current freely to pass therethrough, so that temperature does not rise at the connected portion of the electrode assembly. Moreover, even when said connected portion comes near an electric arc, there is no possibility of the tip end of the assembly falling off due to the strong resilient force of the cylindrical socket.

The resilient force and mechanical strength of said socket part are sufficiently great to absorb any slight variation in the diameters of both members, eliminating the necessity of acculately adjusting these diameters in advance. Therefore, the industrial production of the carbon electrode of the present invention is far easier and more economical than is possible with the U.S. Pat. No. 3,399,322.

As mentioned before, the carbon electrodes of the present invention can be handled in a very easy and simple manner while they are joined in gouging, ensuring the firm coupling of electrodes first by a free insertion and then aforceful pushing with a new electrode slightly rotated. The firm coupling of these electrodes results from the frictional force prevailing at the carbon-to-carbon contact combined with the resilient force prevailing at the copper-to-copper contact, thus enabling carbon electrodes to be joined with a greater mechanical strength and higher electrical conductivity than is possible with the prior art.

I claim:

1. A successively joinable carbon electrode for gouging metallic articles, comprising:

an electrode body coated on its outer periphery with a thin copper layer;

a substantially coaxial projection formed at one end of the electrode body comprising a continuous combination of:

a substantially cylindrical base part integrally formed with the electrode body, and coated on its peripheral surface with a slightly tapered thin copper layer, which is continuous with the copper layer on the outer periphery of the electrode body, the tapered layer being thicker at the portion where said base part meets said electrode body; and

a noncoated frustoconical top part;

a substantially coaxial socket provided inside of the other end of the electrode body in a substantially similar shape to said projection except for the slightly tapered copper coating on said projection, said socket including:

a substantially cylindrical open upper part having a substantially unifonn thickness copper layer on the inner wall thereof which is continuous with the copper layer on the outer periphery of the electrode body; a noncoated frustoconical bottom part; and a slot cut throughout the longitudinal length of the wall of said electrode body defining said cylindrical open part;

wherein the inner diameter of the cylindrical open part of said socket is slightly smaller than the largest outer diameter tapered portion of said coated cylindrical base part of the projection so that said tapered copper layer on said base part closely conforms with the copper layer on the cylindrical open part of said socket upon joining of electrodes, and the total length of said projection is smaller than the total depth of said socket.

2. The carbon electrode as defined in claim 1 wherein the cylindrical base part of the projection has a diameter of from 60 to 70 percent of that of the electrode body.

3. The carbon electrode as defined in claim 1 wherein said projection has a total length of from to percent of the electrode diameter.

4. The carbon electrode as defined in claim I wherein the open cylindrical part of the socket has a depth a little smaller than the length of the substantially cylindrical base part of the projection.

5. The carbon electrode as defined in claim 1 wherein the substantially cylindrical base part of the projection has a length of from 40 to 60 percent of the total length of the projection.

6. The carbon electrode as defined in claim 1 wherein the frustoconical parts of the projection and corresponding socket are tapered at the same included angle of from 12 to 18.

t l l i 

1. A successively joinable carbon electrode for gouging metallic articles, comprising: an electrode body coated on its outer periphery with a thin copper layer; a substantially coaxial projection formed at one end of the electrode body comprising a continuous combination of: a substantially cylindrical base part integrally formed with the electrode body, and coated on its peripheRal surface with a slightly tapered thin copper layer, which is continuous with the copper layer on the outer periphery of the electrode body, the tapered layer being thicker at the portion where said base part meets said electrode body; and a noncoated frustoconical top part; a substantially coaxial socket provided inside of the other end of the electrode body in a substantially similar shape to said projection except for the slightly tapered copper coating on said projection, said socket including: a substantially cylindrical open upper part having a substantially uniform thickness copper layer on the inner wall thereof which is continuous with the copper layer on the outer periphery of the electrode body; a noncoated frustoconical bottom part; and a slot cut throughout the longitudinal length of the wall of said electrode body defining said cylindrical open part; wherein the inner diameter of the cylindrical open part of said socket is slightly smaller than the largest outer diameter tapered portion of said coated cylindrical base part of the projection so that said tapered copper layer on said base part closely conforms with the copper layer on the cylindrical open part of said socket upon joining of electrodes, and the total length of said projection is smaller than the total depth of said socket.
 2. The carbon electrode as defined in claim 1 wherein the cylindrical base part of the projection has a diameter of from 60 to 70 percent of that of the electrode body.
 3. The carbon electrode as defined in claim 1 wherein said projection has a total length of from 80 to 120 percent of the electrode diameter.
 4. The carbon electrode as defined in claim 1 wherein the open cylindrical part of the socket has a depth a little smaller than the length of the substantially cylindrical base part of the projection.
 5. The carbon electrode as defined in claim 1 wherein the substantially cylindrical base part of the projection has a length of from 40 to 60 percent of the total length of the projection.
 6. The carbon electrode as defined in claim 1 wherein the frustoconical parts of the projection and corresponding socket are tapered at the same included angle of from 12* to 18*. 